The present invention relates to typewriters, and more particularly to a ribbon feed mechanism operable to incrementally feed the ribbon by a dual segment continuous motion.
Typewriters with different ribbon feed requirements have prompted the development of feed systems with different characteristics. For example, a U.S. Pat. No. 3,444,979 granted to Bernardino Francisco on May 20, 1969 teaches a ribbon feeding device that insures efficient use of a printing ribbon by compensating for the variation in widths of characters being printed. The ribbon in the Francisco device is advanced by parallel pawls which are reciprocated to alternately engage a ratchet feed during a typing operation to provide two increment feeding. The ribbon is advanced a minor increment by the first pawl during the forward stroke of the pawls when one group of type is printed. The ribbon is advanced a major increment by the second pawl during the return stroke of the pawls when a second group of type is printed. A U.S. Pat. No. 3,788,442 granted to Lehnhardt Jr. et al on Jan. 29, 1974 discloses a cam operated ribbon mechanism for adhesive erase ribbon. A pre-print feed increment and a post-print feed increment of the erase ribbon is provided to prevent the adhesive ribbon from contacting adjacent structures in the typewriter. Both of the foregoing examples teach a dual increment ribbon feed for different ribbon systems. Neither system of the foregoing examples is a continuous ribbon feed and neither system allows for the use of a non-precise mechanism to accomplish a precise incremental ribbon feed as does the instant invention. Furthermore, the same power that is provided for the initial ribbon feed segment of the instant invention is also used for the final ribbon feed segment. Moreover, the power generated to drive the ribbon mechanism the initial segment is substantially reduced to drive the ribbon mechanism the final segment due to a spring urged cam follower rapidly displacing along the cam surface of a tooth on the multi-toothed cam. The reduced power minimizes wear between a power roll and an engaging pawl to drive the ribbon mechanism.